diff options
| author | Eric Dumazet <edumazet@google.com> | 2023-10-20 12:57:47 +0000 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2023-10-23 09:35:01 +0100 |
| commit | 614e8316aa4cafba3e204cb8ee48bd12b92f3d93 (patch) | |
| tree | bc6f18ff35ef1e418218dc944a48aa6d143ae45a /include/linux/tcp.h | |
| parent | af7721448a609d1912b57c825194ef6e17fc71a4 (diff) | |
tcp: add support for usec resolution in TCP TS values
Back in 2015, Van Jacobson suggested to use usec resolution in TCP TS values.
This has been implemented in our private kernels.
Goals were :
1) better observability of delays in networking stacks.
2) better disambiguation of events based on TSval/ecr values.
3) building block for congestion control modules needing usec resolution.
Back then we implemented a schem based on private SYN options
to negotiate the feature.
For upstream submission, we chose to use a route attribute,
because this feature is probably going to be used in private
networks [1] [2].
ip route add 10/8 ... features tcp_usec_ts
Note that RFC 7323 recommends a
"timestamp clock frequency in the range 1 ms to 1 sec per tick.",
but also mentions
"the maximum acceptable clock frequency is one tick every 59 ns."
[1] Unfortunately RFC 7323 5.5 (Outdated Timestamps) suggests
to invalidate TS.Recent values after a flow was idle for more
than 24 days. This is the part making usec_ts a problem
for peers following this recommendation for long living
idle flows.
[2] Attempts to standardize usec ts went nowhere:
https://www.ietf.org/proceedings/97/slides/slides-97-tcpm-tcp-options-for-low-latency-00.pdf
https://datatracker.ietf.org/doc/draft-wang-tcpm-low-latency-opt/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/tcp.h')
| -rw-r--r-- | include/linux/tcp.h | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/include/linux/tcp.h b/include/linux/tcp.h index 04a0e647ef74..6df715b6e51d 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -152,6 +152,7 @@ struct tcp_request_sock { u64 snt_synack; /* first SYNACK sent time */ bool tfo_listener; bool is_mptcp; + s8 req_usec_ts; #if IS_ENABLED(CONFIG_MPTCP) bool drop_req; #endif @@ -257,7 +258,8 @@ struct tcp_sock { u8 compressed_ack; u8 dup_ack_counter:2, tlp_retrans:1, /* TLP is a retransmission */ - unused:5; + tcp_usec_ts:1, /* TSval values in usec */ + unused:4; u32 chrono_start; /* Start time in jiffies of a TCP chrono */ u32 chrono_stat[3]; /* Time in jiffies for chrono_stat stats */ u8 chrono_type:2, /* current chronograph type */ |